The present application relates to pressure sensors for the tires of automobile vehicles.
In order to ensure the safety of automobile vehicles, their tires are fitted with pressure sensors connected by radio to the on-board computer in order to signal any fault. The sensor housed inside the tire is powered by a battery. In order to retain the autonomy of the battery of the sensor, which is inaccessible, this sensor operates only in a cyclical manner, i.e. it has a timing circuit, for activation purposes, which has a very low power consumption and which cyclically activates a microprocessor for a short period, this microprocessor measuring the pressure and temperature and transmitting these measurements by radio.
A wheel rim carrying the sensor can reach high temperatures in the case of repeated intense braking and the microprocessor of the sensor is thus heated to a temperature of about one hundred degrees Celsius.
This temperature exceeds the limit at which industrial standard integrated circuits can be guaranteed to operate properly. There are military standard integrated circuits with a wider operating temperature range but they are naturally more expensive.
A solution has therefore been required to avoid the risk of the thermal destruction of the circuits by operation outside their thermal range.
An earlier solution presented in the application FR 00 12 657 proposes a tire pressure sensor for an automobile vehicle having a module for activating a microprocessor for measuring and controlling radio transmission circuits and temperature-sensitive inhibiting means to inhibit the activation module. This solution consists of using the activation module as a switch for the operation of the microprocessor so that cyclical operation takes place only if the temperature does not exceed a specific threshold.
The major disadvantage of this system is derived from the difficulty in regulating the threshold and the period of the cycle in dependence, principally, upon the integrated circuits used, the specifications of the manufacturers and assembly and/or usage adjustments.
Furthermore, automobile vehicles are assembled on automatic vehicle assembly lines which include a manual step of teaching the vehicle's on-board computer the identification numbers of the wheels and their corresponding location on the vehicle. This manual operation is normally carried out at a diagnostic station integrated into the vehicle assembly line and wheel assembly line for these vehicles, taking into account the fact that a precise location of the wheel on the vehicle corresponds to the position of a wheel in the wheel assembly line.